Session
Session
Session
provides a global object on the client that you can use to store an arbitrary set of key-value pairs. Use it to store things like the currently selected item in a list.
What’s special about Session
is that it’s reactive. If you call Session.get
('currentList')
from inside a template, the template will automatically be rerendered whenever Session.set
('currentList', x)
is called.
To add Session
to your application, run this command in your terminal:
meteor add session
Client Session.set(key, value)
import { Session } from 'meteor/session'
(session/session.js, line 6)
import { Session } from 'meteor/session'
(session/session.js, line 6) Set a variable in the session. Notify any listeners that the value has changed (eg: redraw templates, and rerun any Tracker.autorun
computations, that called Session.get
on this key
.)
Arguments
-
key
String -
The key to set, eg,
selectedItem
-
value
EJSON-able Object or undefined -
The new value for
key
Example:
Tracker.autorun(() => { Meteor.subscribe('chatHistory', { room: Session.get('currentRoomId') }); }); // Causes the function passed to `Tracker.autorun` to be rerun, so that the // 'chatHistory' subscription is moved to the room 'home'. Session.set('currentRoomId', 'home');
Session.set
can also be called with an object of keys and values, which is equivalent to calling Session.set
individually on each key/value pair.
Session.set({ a: 'foo', b: 'bar' });
Client Session.setDefault(key, value)
import { Session } from 'meteor/session'
(session/session.js, line 18)
import { Session } from 'meteor/session'
(session/session.js, line 18) Set a variable in the session if it hasn't been set before. Otherwise works exactly the same as Session.set
.
Arguments
-
key
String -
The key to set, eg,
selectedItem
-
value
EJSON-able Object or undefined -
The new value for
key
This is useful in initialization code, to avoid re-initializing a session variable every time a new version of your app is loaded.
Client Session.get(key)
import { Session } from 'meteor/session'
(session/session.js, line 28)
import { Session } from 'meteor/session'
(session/session.js, line 28) Get the value of a session variable. If inside a reactive computation, invalidate the computation the next time the value of the variable is changed by Session.set
. This returns a clone of the session value, so if it's an object or an array, mutating the returned value has no effect on the value stored in the session.
Arguments
-
key
String -
The name of the session variable to return
Example:
<!-- main.html --> <template name="main"> <p>We've always been at war with {{theEnemy}}.</p> </template>
// main.js Template.main.helpers({ theEnemy() { return Session.get('enemy'); } }); Session.set('enemy', 'Eastasia'); // Page will say "We've always been at war with Eastasia" Session.set('enemy', 'Eurasia'); // Page will change to say "We've always been at war with Eurasia"
Client Session.equals(key, value)
import { Session } from 'meteor/session'
(session/session.js, line 41)
import { Session } from 'meteor/session'
(session/session.js, line 41) Test if a session variable is equal to a value. If inside a reactive computation, invalidate the computation the next time the variable changes to or from the value.
Arguments
-
key
String -
The name of the session variable to test
-
value
String, Number, Boolean, null, or undefined -
The value to test against
If value is a scalar, then these two expressions do the same thing:
Session.get('key') === value Session.equals('key', value)
…but the second one is always better. It triggers fewer invalidations (template redraws), making your program more efficient.
Example:
<template name="postsView"> {{! Show a dynamically updating list of items. Let the user click on an item to select it. The selected item is given a CSS class, so it can be rendered differently. }} {{#each posts}} {{> postItem}} {{/each}} </template> <template name="postItem"> <div class="{{postClass}}">{{title}}</div> </template>
Template.postsView.helpers({ posts() { return Posts.find(); } }); Template.postItem.helpers({ postClass() { return Session.equals('selectedPost', this._id) ? 'selected' : ''; } }); Template.postItem.events({ 'click'() { Session.set('selectedPost', this._id); } });
Using Session.equals here means that when the user clicks on an item and changes the selection, only the newly selected and the newly unselected items are re-rendered.
If Session.get had been used instead of Session.equals, then when the selection changed, all the items would be re-rendered.
For object and array session values, you cannot use Session.equals
; instead, you need to use the underscore
package and write _.isEqual(Session.get(key), value)
.
© 2011–2017 Meteor Development Group, Inc.
Licensed under the MIT License.
https://docs.meteor.com/v1.4.4/api/session.html